The present invention relates in general to detection circuits and, more particularly, to detecting proper operation of a solenoid.
Electrical solenoids form an integral part of many types of mechanical systems. The electric solenoid includes a field coil that develops a magnetic field in response to current flow through the coil. The magnetic field causes movement of an actuator positioned within the field coil that in turn is attached to a mechanical device such as a valve or gear. By activating a switching circuit, current flows through the field coil to develop the magnetic field and move the actuator. For example, in automotive applications, solenoids are often used to shift gears in the transmission or engage emission control subsystems. In industrial applications, the solenoid may be used to open and close valves in hydraulic lines.
As with most physical devices, solenoids are subject to failure. In many applications it is important to know that the actuator has indeed engaged. For example, federal law requires warning indicators if emission control subsystems fail to properly engage. In the prior art the actuator sensing has been accomplished by pressure sensors, Hall-effect sensors and optoelectronic sensors. In the pressure sensor approach, the pressure sensor detects pressures on opposite sides of the valve. When the valve is open, the pressures on opposite sides of the valve equalize and the pressure sensor indicates a zero differential reading. When the valve is closed, the pressures are generally unequal and the pressure sensor reads the difference. However, even with the closed valve, the pressures on opposite sides of the valve may still be the same causing the pressure sensor to inaccurately indicate an open valve. Moreover, pressure sensors have proven expensive and unreliable in harsh environments such as automotive and industrial applications.
The prior art actuator detectors are designed into the original equipment and generally cannot be added on later without extensive re-design. Therefore, it is often impractical to upgrade existing systems to new technology in actuator detection.
Hence, a need exists for a simple and reliable actuator detector that can be integrated into existing systems.